International Journal of Prosthodontics and Restorative Dentistry
Volume 11 | Issue 3 | Year 2021

A Novel Impression Technique for Transforming an Acrylic Hybrid Prosthesis into a Metal Ceramic One Using Combined Analog and Digital Workflows

Hani Tohme1, Ghida Lawand2, Mohammed Akl3

1Department of Removable Prosthodontics, Saint Joseph University, Beirut, Lebanon
2Department of Prosthodontics and Esthetic Dentistry, Saint Joseph University, Beirut, Lebanon
3Department of Restorative Sciences, University of Minnesota, Minneapolis, Minnesota, USA

Corresponding Author: Hani Tohme, Department of Removable Prosthodontics, Saint Joseph University, Beirut, Lebanon, Phone: +961 03307910, e-mail:

How to cite this article Tohme H, Lawand G, Akl M. A Novel Impression Technique for Transforming an Acrylic Hybrid Prosthesis into a Metal Ceramic One Using Combined Analog and Digital Workflows. Int J Prosthodont Restor Dent 2021;11(3):138–141.

Source of support: Nil

Conflict of interest: None


Aim and objective: This technique describes a novel method for converting an acrylic hybrid into metal-ceramic using a combined digital and analog workflow.

Background: Although the acrylic hybrid prosthesis treatment modality has been consistently used for decades, complications such as occlusal wear and tooth debonding have brought to light other alternative restorative materials such as the use of zirconia or a metal framework layered with ceramic. Developing a technique that allows clinicians to convert existing acrylic prostheses easily and conveniently into metal-ceramic ones would overcome many of the complications associated with current acrylic hybrids.

Technique: A combined digital and analog workflow are utilized to convert an acrylic hybrid into a metal-ceramic one by making a repositioning impression with the existing prosthesis maintaining the interface fit for the new prosthesis. The metal framework of the new prosthesis was designed and manufactured digitally. After layering the framework with ceramic, the prosthesis is evaluated for ideal fit, occlusion, and esthetics before delivery.

Conclusion: The combined analog and digital workflow for converting an acrylic hybrid to a metal-ceramic prosthesis through a pick-up impression reduces overall chairside time and provides a predictably fitting prosthesis.

Keywords: Clinical technique, Conversion, Digital dentistry, Hybrids, Implant dentistry, Verification jig.


Today, edentulous oral rehabilitation options often gravitate on implants to provide comfortable and stable prostheses to the patient that may be fixed or removable in nature.1,2 Different patient outcomes were reported when comparing fixed to removable complete implant-supported prostheses; however, fewer impediments were noticed with the fixed option due to the alleviated chances of residual ridge resorption, decreased prosthetic maintenance, and increased patient compliance.13 There are various types of fixed complete prostheses that are classified based on the presence of horizontal or vertical composite defects, available prosthetic space, and the nature of the opposing dentition.4,5 For cases of pronounced intra-arch space, moderate lack of lip support, and a high lip line, the metal acrylic complete fixed dental prosthesis, initially referred to as a hybrid prosthesis, was introduced.1 Metal acrylic hybrid prostheses gained popularity due to their low dynamic occlusal loading risks, esthetic outcomes, long survival rate, and low cost.68 However, despite the favorable results achieved with such prosthetic rehabilitation options, several mechanical and esthetic complications are frequently observed such as abrasion caused by wear, discoloration due to resin staining, and tooth debonding as a result of the reduced thickness of the acrylic resin available for retention over the metal structure beneath (Fig. 1).811

To circumvent this problem, ceramic layering on a metal framework was suggested in lieu of acrylic resin with denture teeth. This alternative provided higher functional and esthetic outcomes and was met with few biological and mechanical complications, as well as a high prevalence of implant and prosthesis survival.12 While some authors13 have attempted to use the patient’s existing prosthesis as a guide to fabricate a new monolithic zirconia hybrid, the process still entailed making a final impression and pouring a master cast and relying on special cemented cylinders which, hypothetically, ensure a passively fitting final prosthesis. This novel technique describes a step-by-step impression procedure for obtaining immediate passive fit while transforming a metal acrylic hybrid prosthesis to a ceramic-layered hybrid prosthesis using combined conventional and digital workflows.

Fig. 1: Old fractured acrylic hybrid prosthesis

Fig. 2: Intraoral scan of the patient’s maxillary arch with acrylic hybrid prosthesis inserted

Fig. 3: Old prosthesis used to make a repositioning impression with putty consistency PVS. This gives the clinicians control of the material and allows them to keep it away from the screw access holes while adapting it



Transforming an existing metal acrylic hybrid to a layered ceramic hybrid often necessitates going through the entire fabrication process from scratch, including making new impressions with impression copings and verification jigs to check the accuracy of the impressions and to detect incidences of misfits.14 This is often considered time-consuming, especially if it has already been done once before. The technique allows the clinician to utilize the existing information and extrapolate it to fabricate a new prosthesis. Fabricating a repositioning impression using an already existing prosthesis allows the restorative dentist to register the ideal spatial implant positioning without the need for a verification jig as the prosthesis is already in optimum fit with the implants. The practitioner may also discard the use of a tray because the hybrid, being reinforced with a metal bar, is not affected by the dimensional changes of the material or by impression removal distortion. Therefore, the uniform distribution of the material and rigidity of the polyvinyl siloxane material is not a concern, even if a tray was not used. In addition, the incorporation of the digital workflow is advantageous as it no longer necessitates time-consuming procedures and appointments such as the need for record base fabrication, setting of teeth, and forming a silicone index to check the available space for ceramics. The “scan only” files were sufficient for the dental technician to design their full-contour prosthesis and to perform the necessary reduction to create the metal framework.

A thorough examination of the existing acrylic prosthesis in terms of occlusal vertical dimension, function, and esthetics is of paramount importance as it will determine the success of the newly fabricated prosthesis. It is also noteworthy to mention that the intaglio surface of the prosthesis should be in intimate contact with the tissue. If a gap is detected, light-body addition silicone must be injected into this space to re-create this intimate contact between the prosthesis and the soft tissue before fabricating the putty silicone matrix for prosthesis pick-up.

The technique presented has multiple limitations that should be considered. The initial chairside time is quite significant as the patient must wait for the setting of the cast before they can receive their prosthesis back after it has been retrieved from the poured pick-up matrix. Furthermore, the cost for fabricating a metal bar and layering it with ceramic by a master ceramist may be significant in some regions like North America, making this option difficult to pursue financially for both the patient and the restorative dentist. With the advancement of digital technology and dental materials, pre-processed milled PMMA and monolithic zirconia hybrids are being fabricated and used more often and may eventually make hand-made prostheses like this one mute, as the lab technicians can easily re-mill the digitally designed prosthesis if complications occur. However, although this technique was done to convert acrylic to metal-ceramic, the same principles could theoretically apply for conversions from acrylic to monolithic zirconia hybrid prostheses, making it a useful approach regardless of the end restorative material.

Overall, the use of this technique has resulted in a significantly reduced number and length of appointments in comparison with the conventional impression technique making it highly favored as a treatment approach for both the patient and the restorative dentist. Future research to compare and overlay the three-dimensional positioning and angulation of the implant analogs between the new and old prostheses may be beneficial to validate this technique due to the well-established limitation and subjectivity of clinically determining complete passive fit.


This article describes a combined analog and digital workflow for converting an acrylic hybrid to a metal-ceramic prosthesis with immediate passive fit through a pick-up impression. This reduces overall chairside and appointment time and provides a predictably fitting prosthesis.


The authors thank Details Lab by Jean Noujeim, Mr Roland Noujeim, and Mrs Aline Abou Faical for the design and lab work on this case.


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